1. Field of the Invention
The present invention relates to an imaging apparatus that can perform an automatic focusing (AF) control.
2. Description of the Related Art
The TV-AF system, known as a conventional AF control system applied to a video camera or other imaging apparatus, is configured to extract a predetermined high-frequency component (contrast component) as an AF signal from a video signal and to control a focusing lens to maximize the AF signal. As another type, there is an AF control system configured to perform a focusing control based on a signal from a distance sensor that can measure the distance to an object or a focal deviation.
As discussed in Japanese Patent Application Laid-Open No. 2002-258147, the above-described TV-AF system and the AF control system using a distance sensor can be combined to realize a hybrid AF control. In general, the TV-AF system can perform a precise focusing control. However, the TV-AF system requires a long focusing time to detect a lens position where the AF signal can be maximized. On the other hand, the AF control system using a distance sensor can reduce the focusing time.
As discussed in Japanese Patent Application Laid-Open No. 2002-258147, an internal measuring system is usable for the AF control performed based on a separately provided distance sensor. According to the internal measuring system, light having entered an imaging optical system is split by a beam splitting mechanism and the split beam is input into the distance sensor to measure the deviation of a focus.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 2002-258147, an external measuring system is employable for the AF control system that includes an imaging optical system and a distance sensor which are separately provided.
According to the above-described internal measuring system, the distance sensor can directly receive an object image captured by the imaging optical system. Thus, the distance sensor does not fail to capture an object. However, the body size of a lens barrel (or the imaging apparatus) tends to become large because the beam splitting mechanism and the distance sensor are installed in the lens barrel.
On the other hand, the external measuring system can provide a higher degree of freedom in the layout because the imaging optical system and the distance sensor are independently disposed. As a result, the external measuring system can realize a compact apparatus.
As described above, if a focusing control based on a distance sensor is combined with a focusing control based on the TV-AF system, an in-focus position of the focusing lens can be speedily detected and the entire focusing time can be reduced.
However, the above-described external measuring system has a problem arising from parallax between an optical axis of the imaging optical system and a measuring axis of the distance sensor, because the distance sensor and the imaging optical system are located independent from each other. In particular, when a zoom position is set to a telephoto side, the angle of view becomes so narrower that the distance sensor may capture an object different from a principal object captured by the imaging optical system.
Furthermore, if the zoom position is set to a telephoto side, the TV-AF system extracts an AF signal (high-frequency component) in a narrow range. Thus, the range for extracting an AF signal may deviate from the measuring axis of the distance sensor. The focus control may not be performed accurately.